If you're eating enough animal protein, the added BCAAs are not going to give you anything that you don't already have/are getting. BCAAs are more important for those who are on an extreme deficit and lifting heavy (wanting to keep muscle mass) or a low protein diet (such as vegan, vegetarian, ect). BCAAs are irrelevant to muscle definition. Fat loss and body percentage determines definition.

Do they give more muscle definition even if I stay with my current weight lifting regime?
*thats what I'm looking to get from using them ;-)

Will it even help with muscle definition from sprinting exercises or just weight lifting?

When have you found the best time to take them and do you go off body weight for the amount you take?

Does it help with burn off unneeded insulation?
:-)
Thank you!!

Most of the time I've heard of BCAAs being used is for muscle sparing regimens regarding intermittent fasting. If your workout in a fasted state, you take them one or two hours (during your fast) before you train, then you train (in a fasted state) and then you eat your post workout meal.
I used to take them but figured they made little difference and cost a lot of money. I lost 20 pounds and got more definition by just stopping eating grains and for the most part ate meat and vegetables. The BCAAs didn't help with definition--didn't hurt it either but I'm not wasting money in that particular way any more.

BCAA's are useful for muscle protein synthesis. If you want to be more defined, you can grow more muscle and obscure it with less adipose tissue. BCAA's may help with the former (unless you're already getting adequate quantities of the BCAA's through other protein sources, such as whey, in which case they won't do much of anything for you), but not the latter.